A digital power source controller may be used for a power source that outputs a constant voltage, and generally encounters input disturbance and output disturbance. To eliminate the input disturbance, a feedforward technology is generally used. There are multiple manners for an implementation method, such as pure digital feedforward; or control is performed in peak current mode. However, the peak current mode is antilogical for dynamic load adjustment (that is, when a load current increases, a duty cycle decreases instead), which affects the feedforward sensitivity to satisfy a dynamic requirement, and reduces a capability of suppressing the input disturbance. Therefore it is difficult to strike a balance between output disturbance suppression and input disturbance suppression. In an application of an isolated power source, for ease of communication, output current detection, and output voltage feedback, a controller is generally placed on a secondary side. Therefore, in various feedforward manners, an input voltage detection problem occurs, and in particular, it is a difficult choice to use setting of a digital feedforward sampling point.